1. Field of the Invention
The present invention relates to a multipoint television conference system for a television conference held among television conference rooms by using a multipoint control unit connected with the television conference rooms through a communication network. In particular, the present invention relates to the multipoint television conference system operating in case where a television conference room intends to intermediately participate in the television conference having been held.
2. Description of the Related Art
The multipoint television (TV) conference system is used in the business world. The system is composed of a plurality of TV conference terminals, which will be called "CTs" hereinafter, and a multipoint control unit, which will be called "MCU" hereinafter, connected with the CTs through a communication network such as a telephone network. The MCU is provided to the system for smoothly carrying out the TV conference among TV conference rooms. The CT is placed in the TV conference room and consists of an operation unit for performing operation concerning with the progress of the TV conference through the MCU, image input-output means and voice input-output means. The image input-output means includes a TV camera for picking up an image of persons (participants of the TV conference) and/or conference material such as documents in the TV conference room and a TV monitor for displaying the same in other TV conference rooms. The voice input-output means includes microphones for picking up voice of the persons in the TV conference room and a speaker for producing voice of other persons in other TV conference rooms.
By virtue of applying the multipoint TV conference system to the TV conference, the process of handling voice and image signals of the system has been developed. For example, by virtue of the MCU, voice signals produced from the TV conference rooms are mixed and sent to the TV conference rooms expect a voice signal produced from the TV conference room of the talker and an image signal produced from a TV conference room of a talker is distributed to other conference rooms of listeners and image signals of listeners in other conference rooms are selected to an image signal of a designated lister by the talker, so that the selected image signal is sent to the TV conference room of the talker.
In order to hold a TV conference, there have been two ways in the multipoint TV conference system. One is a way of calling the TV conference rooms prearranged to participate in the TV conference through the MCU. The TV conference rooms prearranged to participate in the TV conference will be called "TV conference rooms prearranged for participation" hereinafter. In this case, a promoter of the TV conference makes connection among the TV conference room prearranged for participation by telephone calling through the MCU. The other is a way of making the MCU select the TV conference rooms prearranged for participation from the TV conference rooms registered in the MCU and call the TV conference rooms prearranged for participation. In this case, the names of the TV conference rooms are previously registered in the MCU, and the names of the TV conference rooms prearranged for participation can be selected from the previously registered names. When all TV conference rooms prearranged for participation replay to the call and make connection with the MCU respectively, the TV conference can be held. The TV conference rooms which participate in the TV conference will be called "TV conference participating rooms" hereinafter.
The holding circumstance of TV conferences in the multipoint TV conference system is made known to all TV conference rooms in the system by the MCU. The MCU reads the names of the TV conference participating rooms from the register and writes the names into memories of the CTs in all TV conference participating rooms. Therefore, a TV conference room requires to intermediately participate in the TV conference, which will be called "TV conference room requiring intermediate participation" of "TV conference room requiring the intermediate participation" hereinafter, can participates in the TV conference after investigating the names registered in the CT. Meanwhile, when a TV conference participating room intermediately leaves the TV conference, the leaving can be performed by removing the name from the register by operating the CT. As a matter of course, the names rewritten thus in the register are informed to the CTs in all TV conference rooms by the MCU. This system has been disclosed in Japanese Laid-Open Patent Application TOKKAI HEI 4-290361 in 1992.
However, the above prior art multipoint TV conference system has problems. That is, a lot of operation are required to the CTs in the TV conference rooms for holding the TV conference and participating in the TV conference. Usually the TV conference rooms are separated to a plurality of TV conference groups, so that each TV conference room has to select a group and memory the name of the group. Further more, even though the names of the TV conference participating rooms are informed to the TV conference rooms for confirmation, there is no information on a TV conference room not participating in the TV conference and a TV conference room intermediately participate in the TV conference. In particular, regarding the intermediate participation, the TV conference participating rooms are impossible to deny the intermediate participation.